NIST Technical Note 1337: Characterization of Clocks and Oscillators

7. PHASE NOISE AND AM NOISE MEASUREMENTS 287V. ConclusionThe fundamentals and techniques for measurement of phase noise havebeen set forth for two basic systems. The two-oscillator technique providesthe capability for measuring high-performance cw sources. The systemsensitivity is superior to the single-oscillator technique for measuring phasenoise very close to the carrier.High-stability sources such as those used in frequency standards applicationscan be measured without using phase-locked loops. However, mostmicrowave sources exhibit frequency instability that requires phase-lockedloops to maintain the necessary quadrature conditions. The characteristicsof the phase-locked loops must be evaluated to obtain the source phasenoise characteristics. Also. in principle, one must have three sources at thesame frequency to characterize a given source. If three sources are not available,one must assume that either one source is superior in performance orthat they have equal phase noise contributions.The single-oscillator technique employing the delay line as an FM discriminatorhas adequate sensitivity for measuring most microwave sources.The economic advantages of using this system include the fact that onlyone source is required, phase-locked loops are not required, system configurationis relatively inexpensive, and the system is inherently insensitive tooscillator frequency drift.The single-oscillator technique using the delay-line discriminator canbe adapted to measure the phase noise of pulsed sources. Pulsed sourceshave been measured at 94 GHz by F. Labaar at TRW. Redondo Beach,California.ACKNOWLEDGMENTSOur inItial preparations for developing a phase noise measurement capability were the resultof discussions WIth Dr. 10rg Raue of TRW. Our first phase noise development effort wasassisting in the evaluauon of phase noise measurement systems designed and developed byBill Hook of TRW (Hook, 1973). The efforts of Don Leavill ofTRW were vital in initiating themeasurement program.We are very grateful to Dr. Donald Halford of the National Bureau ofStandards in Boulder,Colorado, for his interest, consuhauons, and valuable suggestions during the development ofthe phase noise measurement systems at TRW.We appreciate the measurement cross-checks perfonned by C. Reynolds. 1. Oliverio. andH. Cole of the Hewlett-Packard Company. Dr. 1. Robert Ashley of the University of Colorado.ColoradO Springs, and G. Rast of the U.S. Army Missile Command, Redstone Arsenal,Huntsville, Alabama.REFERENCESAllen. D. W. ([966). Proc.IEEE54. 221-230.Ashley. 1. R.. Searles, C. B.. and Palka. F. M. (1968). IEEE Trans. Microwave Theory Tech.MlT-I6(9),753-760.TN-238